Publication Date:
2016-02-27
Description:
Changes in environmental conditions, such as those caused by elevated carbon dioxide (CO 2 ), potentially alter the outcome of competitive interactions between species. This study aimed to understand how elevated CO 2 could influence competitive interactions between hard and soft corals, by investigating growth and photosynthetic activity of Porites cylindrica (a hard coral) under elevated CO 2 and in the presence of another hard coral and two soft coral competitors. Corals were collected from reefs around Orpheus and Pelorus Islands on the Great Barrier Reef, Australia. They were then exposed to elevated p CO 2 for 4 weeks with two CO 2 treatments: intermediate ( p CO 2 648) and high ( p CO 2 1003) compared with a control (unmanipulated seawater) treatment ( p CO 2 358). Porites cylindrica growth did not vary among p CO 2 treatments, regardless of the presence and type of competitors, nor was the growth of another hard coral species, Acropora cerealis , affected by p CO 2 treatment. Photosynthetic rates of P. cylindrica were sensitive to variations in p CO 2 , and varied between the side of the fragment facing the competitors vs. the side facing away from the competitor. However, variation in photosynthetic rates depended on p CO 2 treatment, competitor identity, and whether the photosynthetic yields were measured as maximum or effective photosynthetic yield. This study suggests that elevated CO 2 may impair photosynthetic activity, but not growth, of a hard coral under competition and confirms the hypothesis that soft corals are generally resistant to elevated CO 2 . Overall, our results indicate that shifts in the species composition in coral communities as a result of elevated CO 2 could be more strongly related to the individual tolerance of different species rather than a result of competitive interactions between species.
Print ISSN:
1054-3139
Electronic ISSN:
1095-9289
Topics:
Biology
,
Geosciences
,
Physics
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